Coated sheet, method of formation thereof, and articles derived therefrom

ABSTRACT

A sheet material includes a polycarbonate substrate and a protective coating containing the reaction products of an aminoplast resin, a polyol compound, and a UV-absorbing amount of a triazine compound. The sheet material exhibits an improved balance of abrasion resistance, solvent resistance, weatherability, and formability.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S.Nonprovisional patent application Ser. No. 10/882,530, filed Jun. 30,2004, now U.S. Pat. No. 7,960,031 issued Jun. 14, 2011, the contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Protective coatings containing the curing products of aminoplast resinsand polyvalent alcohols are known to improve the abrasion resistance andsolvent resistance of thermoplastic substrates. For example, U.S. Pat.No. 5,552,936 to Moore generally describes a protective coatingcomposition containing a polycaprolactone polyol and an aminoplastderivative. As another example, U.S. Pat. No. 4,714,657 to Quinn et al.describes protective coatings derived from polyester polyols andaminoplast derivatives. Another example is provided by U.S. Pat. No.4,913,974 to Moore et al., which describes coated articles comprising athermoplastic substrate and a surface coating that is the reactionproduct of a melamine compound, a polyol, and a multimeric benzotriazolecompound. Increasingly demanding product applications have created aneed for coated thermoplastic sheets with an improved balance ofabrasion resistance, solvent resistance, weatherability, andformability.

BRIEF DESCRIPTION OF THE INVENTION

An improved balance of abrasion resistance, solvent resistance,weatherability, and formability is provided by a sheet, comprising: afirst layer comprising a polycarbonate resin; and a second layerdisposed on a surface of the first layer, the second layer comprising acured product obtained on curing a curable composition comprising anaminoplast resin, a polyol compound, and a UV-absorbing amount of atriazine compound.

Other embodiments, including a method of producing the sheet, and anarticle derived from the sheet, are described in detail below.

DETAILED DESCRIPTION OF THE INVENTION

The present inventors have conducted extensive research into improvingthe properties of polycarbonate sheet with protective coatings. It isknown that a key factor in determining the weathering lifetime of acoating is the stability of the ultraviolet light absorber (“UVabsorber”) within the coating. See, for example, D. R. Bauer, Journal ofCoatings Technology, vol. 69, pp. 85-95 (1997); and J. E. Pickett in“Handbook of Polymer Degradation, 2^(nd) Edition,” S. H. Hamid, ed.,Marcel Dekker (2000) pp. 163-190. However, the kinetics of UV absorberloss through photolysis were shown to be dependent on the structure ofthe UV absorber and on the matrix, and the performance of a particularabsorber in a particular coating could not be accurately predicted apriori. The literature also indicates that although triazine UVabsorbers may be about 30% more stable than benzotriazole UV absorbersin some protective coatings, they may be as much as 2.5 times lessstable in others.

The present inventors were therefore surprised to discover thataminoplast/polyol protective coatings containing triazine-based UVabsorbers show substantially superior light stability compared tocorresponding coatings with benzotriazole- or benzophenone-based UVabsorbers. Also surprising was the unexpected improvement in theformability of the sheets with protective coatings containingtriazine-based UV absorbers without loss of abrasion resistance. The UVabsorber constitutes such a small percentage of the protective coatingcomposition that it was not expected to have any significant effect onformability. In addition, the protective coatings containingtriazine-based UV absorbers unexpectedly exhibit improved coatingadhesion.

Thus, one embodiment is a sheet, comprising: a first layer comprising apolycarbonate resin; and a second layer disposed on a surface of thefirst layer, the second layer comprising a cured product obtained oncuring a curable composition comprising an aminoplast resin, a polyolcompound, and a UV-absorbing amount of a triazine compound.

The sheet comprises a first layer comprising a polycarbonate resin.Suitable polycarbonates may be prepared by reacting a dihydric phenolwith a carbonate precursor, such as phosgene, a haloformate, or acarbonate ester. Generally, such carbonate polymers comprise recurringstructural units of the formula

wherein A is a divalent aromatic radical of the dihydric phenol employedin the polymer producing reaction. In one embodiment, the polycarbonatemay have an intrinsic viscosity (as measured in methylene chloride at25° C.) of about 0.30 to about 1.00 deciliter/gram (dL/g). The dihydricphenols employed to provide such polycarbonates may be mononuclear orpolynuclear aromatic compounds, containing as functional groups twohydroxy radicals, each of which is attached directly to a carbon atom ofan aromatic nucleus. Suitable dihydric phenols include, for example,2,2-bis(4-hydroxyphenyl)propane (bisphenol A), hydroquinone, resorcinol,2,2-bis(4-hydroxyphenyl)pentane, 2,4′-(dihydroxydiphenyl)methane,bis(2-hydroxyphenyl)methane, bis(4-hydroxyphenyl)methane,bis(4-hydroxy-5-nitrophenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane,3,3-bis(4-hydroxyphenyl)pentane, 2,2-dihydroxydiphenyl,2,6-dihydroxynaphthalene, bis(4-hydroxydiphenyl)sulfone,bis(3,5-diethyl-4-hydroxyphenyl)sulfone,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 2,4′-dihydroxydiphenylsulfone, 5′-chloro-2,4′-dihydroxydiphenyl sulfone,bis(4-hydroxyphenyl)diphenyl sulfone, 4,4′-dihydroxydiphenyl ether,4,4′-dihydroxy-3,3′-dichlorodiphenyl ether,4,4-dihydroxy-2,5-dihydroxydiphenyl ether, and the like, and mixturesthereof. Other dihydric phenols suitable for use in the preparation ofpolycarbonate resins are described, for example, in U.S. Pat. Nos.2,999,835 to Goldberg, 3,334,154 to Kim, and 4,131,575 to Adelmann etal.

The polycarbonate resins can be manufactured by known processes, suchas, for example and as mentioned above, by reacting a dihydric phenolwith a carbonate precursor, such as phosgene, a haloformate, or acarbonate ester, in accordance with methods set forth in the above-citedliterature and in U.S. Pat. No. 4,123,436 to Holub et al., or bytransesterification processes such as are disclosed in U.S. Pat. No.3,153,008 to Fox, as well as other processes known to those skilled inthe art.

It is also possible to employ two or more different dihydric phenols ora copolymer of a dihydric phenol with a glycol or with a hydroxy- oracid-terminated polyester or with a dibasic acid in the event acarbonate copolymer or interpolymer rather than a homopolymer isdesired. Branched polycarbonates are also useful, such as are describedin U.S. Pat. No. 4,001,184 to Scott. Also, there can be utilized blendsof linear polycarbonate and a branched polycarbonate. Moreover, blendsof any of the above materials may be employed in the practice of thisinvention to provide the polycarbonate resin.

The polycarbonates may be branched or linear and generally will have aweight average molecular weight of about 10,000 to about 200,000 atomicmass units (AMU), specifically from about 20,000 to about 100,000 AMU asmeasured by gel permeation chromatography. The polycarbonates of theinvention can employ a variety of end groups to improve performance.Bulky mono phenols, such as cumyl phenol, are preferred.

Suitable polycarbonates further include those derived from bisphenolscontaining alkyl cyclohexane units. Such polycarbonates have structuralunits corresponding to the structure

wherein R^(a)-R^(d) are each independently hydrogen, C₁-C₁₂ hydrocarbyl,or halogen; and R^(e)-R^(i) are each independently hydrogen, C₁-C₁₂hydrocarbyl. As used herein, the term “hydrocarbyl”, whether used byitself, or as a prefix, suffix, or fragment of another term, refers to aresidue that contains only carbon and hydrogen. The residue may bealiphatic or aromatic, straight-chain, cyclic, bicyclic, branched,saturated, or unsaturated. It may also contain combinations ofaliphatic, aromatic, straight chain, cyclic, bicyclic, branched,saturated, and unsaturated hydrocarbon moieties. The hydrocarbylresidue, when so stated however, may contain heteroatoms over and abovethe carbon and hydrogen members of the substituent residue. Thus, whenspecifically noted as containing such heteroatoms, the hydrocarbyl orhydrocarbylene residue may also contain carbonyl groups, amino groups,hydroxyl groups, or the like, or it may contain heteroatoms within thebackbone of the hydrocarbyl residue. Alkyl cyclohexane containingbisphenols, for example the reaction product of two moles of a phenolwith one mole of a hydrogenated isophorone, are useful for makingpolycarbonate resins with high glass transition temperatures and highheat distortion temperatures. Such isophorone bisphenol-containingpolycarbonates have structural units corresponding to the structure

wherein R^(a)-R^(d) are as defined above. These isophorone bisphenolbased resins, including polycarbonate copolymers made containingnon-alkyl cyclohexane bisphenols and blends of alkyl cyclohexylbisphenol containing polycarbonates with non-alkyl cyclohexyl bisphenolpolycarbonates, are supplied by Bayer Co. under the APEC trade name anddescribed, for example, in U.S. Pat. No. 5,034,458 to Serini et al.

The first layer may be substantially transparent, translucent, oropaque. In one embodiment, the first layer comprises at least about 80weight percent polycarbonate, specifically at least about 90 weightpercent polycarbonate, more specifically at least about 95 weightpercent polycarbonate.

In addition to polycarbonate, the first layer may, optionally, comprisean additional thermoplastic resin such as, for example, poly(butyleneterephthalate), poly(ethylene terephthalate), aliphatic polyesters,poly(styrene-co-acrylonitrile), rubber-containing impact modifiers, orthe like, separately or in combinations. The first layer may,optionally, further comprise UV stabilizers, heat stabilizers, and thelike, which are typically present at less than 1 weight percent whenused.

In one embodiment, the first layer is substantially free of colorant. Inother words, the first layer contains less than 0.1 weight percentcolorant. It may be preferred that no intentionally added colorant beused. In another embodiment, the first layer comprises a colorant in anamount up to about 20 weight percent, specifically up to about 5 weightpercent. The term “colorant” includes dyes and pigments and any othersubstances added to affect the hue or increase the opacity of the firstlayer.

In one embodiment, the first layer has a thickness of about 0.05 toabout 25 millimeters. Within this range, the thickness may be at leastabout 0.1 millimeters, more specifically at least about 0.2 millimeters.Also within this range, the thickness may be up to about 20 millimeters,more specifically up to about 13 millimeters.

The sheet comprises a second layer disposed on a surface of the firstlayer. The second layer comprises a cured product obtained on curing acurable composition comprising an aminoplast resin, a polyol compound,and a UV-absorbing amount of a triazine compound.

The aminoplast resin is the reaction product of an amine and analdehyde, optionally in combination with an alcohol. Suitable aminesused to prepare the aminoplast resin include, for example, urea,melamine, triazines, diazines, triazoles, guanidines, guanamines, andthe like, as well as alkyl- and aryl-substituted derivatives of theforegoing amines Suitable aldehydes used to form the aminoplast resininclude, for example, formaldehyde, acetaldehyde, crotonaldehyde,acrolein, benzaldehyde, furfural, and the like. The aminoplasts containmethylol or similar alkylol groups, depending on the structure of thealdehyde used. In one embodiment, at least a portion of the alkylolgroups is etherified by reaction with a monohydric alcohol. Suitablemonohydric alcohols include, for example, C₁-C₈ aliphatic alcohols suchas, for example, ethanol, propanol, butanol, cyclohexanol, and the like.Suitable monohydric alcohols further include alcohols containingaromatic groups, such as benzyl alcohol, and halogen-substitutedalcohols such as 3-chloropropanol. Suitable monohydric alcohols furtherinclude any additional alcohols described below as solvents for thecurable composition.

In one embodiment, the aminoplast is the reaction product of melamine,formaldehyde, and an alcohol, wherein the reaction product has theformula

wherein each occurrence of R¹ is independently hydrogen, a methylenebridge to another melamine nucleus, or CH₂OR², wherein R² is hydrogen orC₁-C₁₂ alkyl. In particular, R² may be methyl. In one embodiment, atleast 4, at least 5, or all 6 R¹ groups may be methoxymethyl.

Suitable aminoplast resins include the urea-formaldehyde resinsavailable from Cytec as CYMEL® U-60, U-64, U-65, and U-382, and themelamine-formaldehyde resins available from Cytec as CYMEL® 300, 301,303, 322, 350, and 3717.

The coating composition may comprise curable solids and volatilesolvents. Thus, the composition may comprise about 20 to about 80 weightpercent of the aminoplast resin, based on the total weight of thecurable solids. Within this range, the aminoplast resin amount mayspecifically at least about 30 weight percent, more specifically atleast about 40 weight percent. Also within this range, the aminoplastresin amount may specifically up to about 70 weight percent, morespecifically up to about 60 weight percent.

The curable solids may be diluted with solvents. Based on total coatingweight (the sum of curable solids and solvents), the weight of curablesolids ranges from about 1 to about 99 weight percent. Within thisrange, the curable solids amount may specifically at least about 10weight percent, more specifically at least about 20 weight percent. Alsowithin this range, the curable solids amount may specifically up toabout 80 weight percent, more specifically up to about 60 weightpercent.

In addition to the aminoplast resin, the curable composition used toform the second layer comprises a polyol compound. The polyol compoundis an organic compound containing at least two hydroxy groups. In oneembodiment, the polyol compound may have the structureHO—R³—OHwherein R³ is C₂-C₂₄ hydrocarbylene, optionally substituted with one ormore heteroatoms. Suitable polyol compounds include dihydric phenols,such as, for example, resorcinol, 2,2′-methylenediphenol,2,4′-methylenediphenol, 4,4′-methylenediphenol,4,4′-isopropylidenediphenol, 4,4′-dihydroxydiphenylsulfone, and thelike; dihydric aliphatic alcohols such as, for example, ethylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol, propyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-penatnediol,1,2,3-propanetriaol, pentaerythritol, sorbitol, and the like; alkydresins, such as hydroxy-functional epoxy resins; soluble cellulosederivatives; vinyl polymers with free hydroxyl groups such ashomopolymers and copolymers of vinyl alcohol, and partial hydrolysatesof homopolymers and copolymers of vinyl acetate; oligomeric aliphaticpolyester diols; oligomeric aliphatic polycarbonate diols; oligomericaliphatic polyestercarbonate diols; oligomeric aliphatic polyurethanediols; and the like; and mixtures of the foregoing polyol compounds. Inone embodiment, the polyol compound may contain carboxyl or amino groupsin addition to the hydroxy groups.

In one embodiment, the polyol compound comprises an oligomeric aliphaticpolyester diol. The oligomeric aliphatic polyester diol may be thereaction product of a diacid and a diol, wherein the diacid comprises atleast 50% by number aliphatic diacids in which the two acid groups areseparated by at least two, preferably at least four, intervening carbonatoms, and the diol comprises at least 50% by number aliphatic diols inwhich the two hydroxyl groups are separated by at least two, preferablyat least four, intervening carbon atoms. Suitable aliphatic diacidsinclude, for example, succinic acid, glutaric acid, adipic acid, subericacid, sebacic acid, azelaic acid, 1,12-dodecanedioic acid, 2,2,4- and2,4,4-trimethyl-1,6-hexanedioic acid, and mixtures thereof. Suitable foruse as the remaining diacids are, for example, unsaturated dicarboxylicacids such as maleic acid, fumaric acid, itaconic acid, citraconic acid,and the like; cycloaliphatic diacids and anhydrides such as1,2-cyclohexanedicarboxylic anhydride, tetrahydrophthalic anhydride,1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, andthe like; aromatic diacids such as phthalic acid, isophthalic acid,terephthalic acid, and the like; and mixtures thereof. Suitable for useas the aliphatic diols are those having the structureHO—(CH₂)_(n)—OHwherein n is 4 to about 12, and C₁-C₆ hydrocarbyl-substitutedderivatives thereof. Specific aliphatic diols include, for example,1,6-hexanediol, 3-methyl-1,5-pentanediol,2,2,4-trimethyl-1,5-pentanediol, and the like. Suitable for use as theremaining diol are, for example, short chain aliphatic diols such as1,3-butanediol, 1,3-propylene glycol, 2,2-diethyl-1,3-propanediol,ethylene glycol, neopentyl glycol, and the like; cycloaliphatic diolssuch as 4,4′-methylenebis(cyclohexanol),4,4′-isopropylidenebis(cyclohexanol), cyclohexanedimethanols, and thelike; aromatic diols such as phenylenedipropanols, and the like; andmixtures thereof. In one embodiment, the oligomeric aliphatic polyesterdiol is a reaction product of an aliphatic diacid in which the two acidgroups are separated by at least four, intervening carbon atoms, and analiphatic diols in which the two hydroxyl groups are separate by atleast four intervening carbon atoms. The oligomeric aliphatic polyesterdiol may also be synthesized by the reaction of an aliphatic lactone,such as caprolactone, with an aliphatic diol. In one embodiment, theoligomeric aliphatic polyester diol has a number average molecularweight of about 200 to about 4,000 AMU. Within this range, the molecularweight may specifically be at least about 500 AMU. Also within thisrange, the molecular weight may specifically be up to about 3,000 AMU,more specifically up to about 2,500 AMU. Suitable techniques forpreparing the oligomeric polyester diols include those known in the artfor preparation of polyesters, generally. Suitable oligomeric aliphaticpolyester diols are commercially available as, for example, DESMOPHEN®S1015-120 from Bayer (formerly sold as RUCOFLEX® S1015-120), and Tone210 from Dow.

In one embodiment, the polyol compound comprises an oligomeric aliphaticpolycarbonate diol. An oligomeric aliphatic polycarbonate diol is areaction product of a diol, as described above for the oligomericaliphatic polyester diol, and a carbonate precursor. As for thesynthesis of polycarbonate, described above, the carbonate precursor mayinclude phosgene, a haloformate, or a carbonate ester. Suitable diolsare the same as those described above for the oligomeric aliphaticpolyester diol. In one embodiment, the oligomeric aliphaticpolycarbonate diol has a number average molecular weight of about 200AMU to about 4,000 AMU. Within this range, the molecular weight mayspecifically be at least about 400 AMU, more specifically at least about800 AMU. Also within this range, the molecular weight may specificallybe up to about 3,000 AMU, more specifically up to about 2,500 AMU.Suitable techniques for preparing the oligomeric polycarbonate diolsinclude those known in the art for preparation of polycarbonates,generally.

In one embodiment, the polyol compound comprises an oligomeric aliphaticpolyestercarbonate diol. Such compounds are essentially hybrids of theoligomeric aliphatic polyester diols and oligomeric aliphaticpolycarbonate diols described above, in that they contain two terminalhydroxy groups and internal carbonate linkages and ester linkages. Inone embodiment, the oligomeric aliphatic polyestercarbonate diol has anumber average molecular weight of at least about 200 AMU. Theoligomeric aliphatic polyestercarbonate diols may be prepared from adiol, a diacid, and a carbonate precursor, using techniques known in theart for the preparation of polyestercarbonates. Suitable oligomericaliphatic polyestercarbonate diols are available, such as, for example,DESMOPHEN® VP LS 2391 (formerly sold as DESMOPHEN® C200) from Bayer.

In one embodiment, the polyol compound comprises an oligomeric aliphaticpolyurethane diol. The oligomeric aliphatic polyurethane diol may havethe structure

wherein R⁴ is the residuum of a diol comprising at least 50% by numberaliphatic diols in which the two hydroxyl groups are separate by atleast two, preferably at least four, intervening carbon atoms; R⁶ is theresiduum of a diisocyanate compound comprising at least 50% by numberaliphatic diisocyanates in which the two isocyanate groups are separateby at least two, preferably at least four, intervening carbon atoms; andp is 2 to about 20. Suitable diols are described above. Suitablealiphatic diisocyanate compounds may have the structureO═C═N—R⁶—N═C═Owherein R⁶ is C₂-C₁₂ alkylene. The oligomeric aliphatic polyurethanediol may be prepared according to procedures known in the art forpreparing polyurethanes. Suitable oligomeric aliphatic polyurethanediols are commercially available as, for example, K-FLEX® UD-320 fromKing Industries.

In one embodiment, the polyol compound comprises any of the diolcompounds described above in combination with a triol compound. Suitabletriol compound include, for example, the trifunctional, oligomericpolycaprolactones available as Tone 301, Tone 305 and Tone 310 from Dow,and the aliphatic polyester triol available as DESMOPHEN® F2037-420 fromBayer. The weight ratio of the diol compound to the triol compound maybe about 1:99 to about 99:1, specifically about 50:50 to about 98:2,more specifically about 80:20 to about 97:3.

The curable composition may comprise about 20 to about 80 weight percentof the polyol compound, based on the total weight of the curable solids.Within this range, the polyol compound amount may specifically be atleast about 30 weight percent, more specifically at least about 40weight percent. Also within this range, the polyol compound amount mayspecifically be up to about 70 weight percent, more specifically up toabout 60 weight percent.

In one embodiment, the curable composition comprises the aminoplastresin and the polyol compound in a weight ratio of about 40:60 to about60:40, more specifically about 45:55 to about 55:45.

In addition to the aminoplast resin and the polyol compound, the curablecomposition comprises a UV-absorbing amount of a triazine compound. Inone embodiment, the triazine compound may have the structure

wherein each occurrence of Ar is independently phenyl or substitutedphenyl; wherein the substituents on the phenyl group may be hydroxy,amino, C₁-C₁₂ hydrocarbyl, C₁-C₁₂ hydrocarbyloxy, or C₁-C₁₂hydrocarbylamino; and R⁷ is hydrogen, C₁-C₁₆ hydrocarbyl wherein thehydrocarbyl group may contain nitrogen or oxygen heteroatoms, or

wherein R⁸ is hydrogen or C₁-C₁₆ hydrocarbyl wherein the hydrocarbylgroup may contain nitrogen or oxygen heteroatoms. Such compounds havereactive hydroxy groups that can react with the aminoplast resin.Suitable triazine compounds further include the unanchored stabilizersdescribed in U.S. Pat. No. 5,621,052 to Szita et al., as well as thosecommercially available from Cytec as CYASORB® UV-1164, CYASORB®UV-1164A, and CYASORB® UV-1164L, and those available from Ciba SpecialtyChemicals as TINUVIN® 400, TINUVIN® 405, and TINUVIN® 1577.

The curable composition comprises sufficient triazine compound to absorbultraviolet light. For example, the curable composition may compriseabout 0.1 to about 10 weight percent of the triazine compound, based onthe total weight of the curable solids. Within this range, the triazinecompound amount may specifically be at least about 1 weight percent,more specifically at least about 1.5 weight percent. Also within thisrange, the triazine compound amount may specifically be up to about 5weight percent, more specifically up to about 4 weight percent.

The curable composition may, optionally, further comprise a hinderedamine light stabilizer. Hindered amine light stabilizers may be 5- or6-membered nitrogen-containing aliphatic heterocycles withtetrasubstituted carbon moieties on either side of the ring nitrogen.The nitrogen can have as its third substituent a hydrogen atom, alkylgroup, alkoxy group, or the like. Examples of many hindered amine lightstabilizers can be found in Plastics Additives Handbook, 5^(th) Edition,H. Zweifel, ed., Hanser Publishers (2001) pp. 123-136. Hindered aminelight stabilizers may include a 2,2,6,6-tetraalkylpiperidine moietyhaving the structure

wherein each occurrence of R⁹ is independently C₁-C₆ alkyl; R¹⁰ ishydrogen or methyl; and each occurrence of R¹¹ is hydrogen, C₁-C₆ alkyl,or C₁-C₆ alkoxy. Many specific examples of hindered amine lightstabilizers may be found in U.S. Pat. No. 5,714,530 to Waterman et al.In one embodiment, the conjugate acid of the hindered amine lightstabilizer has a pK_(a) less than 6.5. Suitable hindered amine lightstabilizers are commercially available, for example, as TINUVIN® 123,TINUVIN® 152 (formerly sold as CGL052), TINUVIN® 622, TINUVIN® 765, andTINUVIN® 770, all from Ciba Specialty Chemicals. When present, thehindered light stabilizer may be used in an amount of about 0.01 toabout 1 weight percent based on the total weight of the curablecomposition. Within this range, the hindered amine light stabilizeramount may specifically be at least about 0.02 weight percent, morespecifically at least about 0.04 weight percent. Also within this range,the hindered amine light stabilizer amount may specifically be up toabout 0.5 weight percent, more specifically up to about 0.3 weightpercent.

The curable composition may, optionally, further comprise a solvent toaid in solubilizing the curable components and coating the composition.Suitable solvents include, for example, C₁-C₁₂ alcohols, C₃-C₁₂ ketones,C₃-C₁₂ esters, C₄-C₁₂ ethers, C₃-C₁₂ alkoxy alkanols, C₁-C₁₂ halogenatedhydrocarbons, C₂-C₁₂ carboxylic acids, C₆-C₁₈ aromatic compounds, or thelike, and mixtures thereof. Particularly suitable compounds include, forexample, C₁-C₁₃ alkanols, and C₃-C₁₃ alkoxyalkanols. For example, thesolvent may comprise methanol, ethanol, n-propanol, n-butanol,1-methoxy-2-propanol, 1-butoxy-2-propanol, or the like, or mixturesthereof. In one embodiment, the solvent comprises 1-methoxy-2-propanol,1-butoxy-2-propanol, or a mixture thereof.

The curable composition may, optionally, further comprise a curingcatalyst. Suitable curing catalysts include, alkyl acid phosphates, suchas monomethyl acid phosphate, monoethyl acid phosphate, monopropyl acidphosphate and monobutyl acid phosphate, as well as the correspondingdialkyl compounds, such as dibutyl acid phosphate. A mixture of mono-and dialkyl acid phosphates is often utilized. In addition to the alkylacid phosphates, examples of other acid catalysts which can be usedinclude phosphoric acid, maleic acid and anhydride, fumaric acid,chloromaleic acid and anhydride, alkyl acid phthalates such as methyl,ethyl, propyl and butyl acid phthalates, monoalkyl succinates andmaleates such as methyl, ethyl, propyl and butyl succinates and maleatesand others having sufficient solubility to permit them to be dissolvedin the coating composition at the desired proportion. Catalysts whichhave been found to be particularly suitable are compounds such as thesulfonic acids and derivatives thereof including, for example,p-toluenesulfonic acid, methylsulfonic acid, sulfamic acid and the like,and mixtures thereof. When present, the curing catalyst may be used inan amount of about 0.1 to about 5 weight percent, based on the totalweight of the curable composition.

When the curable composition comprises a curing catalyst, it may,optionally, further comprise a catalyst stabilizer. Suitable catalyststabilizers include tertiary amines having the structureN(R¹²)₃wherein each R¹² is independently C₁-C₆ hydrocarbyl, or two R¹² groupsmay combine to form a C₂-C₁₂ hydrocarbylene group. In one embodiment,the sum of carbon atoms in the three R¹² groups is about 4 to about 10,more specifically about 5 to about 8. A representative tertiary amine istriethylamine. Suitable catalyst stabilizers further include aromaticheterocyclic amines such as pyridine, aminoalkanols such as2-methylaminoethanol, and the like. Mixtures of the foregoing catalyststabilizers may be employed.

In addition to the components mentioned above, the curable compositionmay, optionally, further comprise an additive selected from flow controlagents, surfactants, viscosity modifiers, antifoaming agents, and thelike, and mixtures thereof.

In one embodiment, the second layer has a thickness of about 1 to about50 micrometers after curing. Within this range, the second layerthickness may specifically be at least 2 micrometers, more specificallyat least 5 micrometers. Also within this range, the second layerthickness may specifically be up to about 40 micrometers, morespecifically up to about 25 micrometers.

The second layer is disposed on a surface of the first layer. In oneembodiment, the second layer is disposed on at least 95%, morespecifically at least 98%, still more specifically at least 99%, of thesurface of the first layer. In one embodiment, a second layer isdisposed on each of two surfaces of the first layer. In anotherembodiment, the second layer is disposed on one surface of the firstlayer. In this embodiment, the surface of the first layer not in contactwith the second layer may be in contact with another layer (e.g., anantifog layer), the contact with the other layer being formed bycoating, lamination, or the like.

One embodiment is a sheet, comprising: a first layer comprising apolycarbonate resin; and a second layer disposed on a surface of thefirst layer, the second layer comprising a cured product obtained oncuring a curable composition comprising

-   -   a melamine-formaldehyde resin,    -   an oligomeric aliphatic polyester diol, an oligomeric aliphatic        polycarbonate diol, an oligomeric aliphatic polyestercarbonate        diol, an oligomeric aliphatic polyurethane diol, or a mixture        thereof, and    -   a UV-absorbing amount of a triazine compound having the        structure

-   -   wherein each occurrence of Ar is independently phenyl or        substituted phenyl;    -   wherein the substituents on the phenyl group may be hydroxy,        amino, C₁-C₁₂ hydrocarbyl, C₁-C₁₂ hydrocarbyloxy, or        hydrocarbylamino; and R⁷ is hydrogen, C₁-C₁₆ hydrocarbyl wherein        the hydrocarbyl group may contain nitrogen or oxygen        heteroatoms, or

-   -   wherein R⁸ is hydrogen or C₁-C₁₆ hydrocarbyl wherein the        hydrocarbyl group may contain nitrogen or oxygen heteroatoms.

Another embodiment is a sheet, comprising: a first layer comprising apolycarbonate resin and having a thickness of about 0.1 to about 20millimeters; and a second layer disposed on a surface of the firstlayer, the second layer having a thickness of about 2 to about 40micrometers and comprising a cured product obtained on curing a curablecomposition comprising, based on the total weight of the curable solids,

-   -   about 40 to about 60 weight percent melamine-formaldehyde resin,    -   about 40 to about 60 weight percent of an oligomeric polyester        diol, an oligomeric polycarbonate diol, an oligomeric        polyestercarbonate diol, or a mixture thereof,    -   about 0.1 to about 5 weight percent of p-toluenesulfonic acid,        and    -   about 0.1 to about 5 weight percent of a UV-absorbing amount of        a triazine compound having the structure

-   -   wherein each occurrence of Ar is independently phenyl or        substituted phenyl;    -   wherein the substituents on the phenyl group may be hydroxy,        amino, C₁-C₁₂ hydrocarbyl, C₁-C₁₂ hydrocarbyloxy, C₁-C₁₂        hydrocarbylamino; and R⁷ is hydrogen, C₁-C₁₆ hydrocarbyl wherein        the hydrocarbyl group may contain nitrogen or oxygen        heteroatoms, or

-   -   wherein R⁸ is hydrogen or C₁-C₁₆ hydrocarbyl wherein the        hydrocarbyl group may contain nitrogen or oxygen heteroatoms.

In one embodiment, the curable composition further comprises a solventcomprising 1-methoxy-2-propanol, 1-butoxy-2-propanol, or a mixturethereof. In one embodiment, the curable composition further comprisesabout 0.01 to about 1 weight percent of a hindered amine lightstabilizer.

The curable composition may be formed by blending the aminoplast resin,the polyol compound, the triazine compound, and any optional components.The curable composition may be applied to the first layer using knownmeans such as, for example, rolling, spraying, dipping, brushing,flow-coating, casting, and the like. The curable coating is preferablycured by heat curing. For example, it may be heated conventionally, byinfrared radiation, microwave radiation, or the like. Curing may beaccomplished, for example, by heating to about 100 to about 150° C. forabout 15 minutes to about 4 hours. In one embodiment, the curingtemperature may be about 130° C. or less to reduce or eliminatedistortion of the first layer. In one embodiment, the solvent issubstantially evaporated before the curing temperature is reached.

One embodiment is a method of producing a sheet, comprising: coating acurable composition on a face of a polycarbonate sheet, wherein thecurable composition comprises an aminoplast resin, a polyol compound,and a UV-absorbing amount of a triazine compound; and curing the curablecomposition to form a protective layer.

One embodiment is an article formed from a coated polycarbonate sheethaving any of the second layer compositions described above. Suitabletechniques for forming articles include, for example, drape-forming,thermoforming, vacuum forming, pressure forming, compression molding,cold curving, hot line bending, lamination, in-mold decoration,printing, and the like, and combinations thereof. Articles that may beformed from the sheet include, for example, motorcycle windshields,goggles, and helmet visors.

Those skilled in the art will also appreciate that common curing andsurface modification processes include, for example, heat-setting,texturing, embossing, corona treatment, flame treatment, plasmatreatment and vacuum deposition may further be applied to the abovearticles to alter surface appearances and impart additionalfunctionalities to the articles.

The invention is further illustrated by the following non-limitingexamples.

Examples 1-35

Coating Formulations. Several curable coating compositions differing inthe types of polyol compound and UV absorber were prepared containing5.3 grams CYMEL® 303 (hexamethoxymethylmelamine; obtained from Cytec),0.15 gram p-toluenesulfonic acid, 6.16 g 1-methoxy-2-propanol, 6.16 g.1-butoxy-2-propanol, 0.59 gram methanol, 0.75 gram 1-butanol, 0.59 g2-propanol, 0.05 g EFKA® 30, and 0.56 g (as solids) UV absorber. The UVabsorber was therefore present at 5% based on coating solids. The polyolcompound was selected from DESMOPHEN® VP LS 2391 (an aliphaticpolyestercarbonate diol available from Bayer), DESMOPHEN® S1015-120 (analiphatic polyester diol available from Bayer), and K-FLEX® UD-320 (analiphatic polyurethane diol available from Bayer). The UV absorbers wereselected from CYASORB® UV-531 (a benzophenone available from Cytec),TINUVIN® 384 (a benzotriazole available from Ciba Specialty Chemicals),TINUVIN® 400 (a triazine available from Ciba Specialty Chemicals), and2,6-dihydroxybenzophenone (DHBP). Some samples additionally containedthe hindered amine light stabilizer TINUVIN® 152, available from CibaSpecialty Chemicals.

Volatility and Migration of UV Absorbers. Samples were flow coated onto2 inch by 6 inch (5.08 centimeter by 15.24 centimeter) unstabilizedpolycarbonate film with a thickness of 10 mils (250 microns). Coatedlayers were allowed to drain for approximately 30 minutes then placed ina 125° C. forced air oven for five minutes to fully dry the film.Initial absorbance (at the λ_(max) of the UV absorber) was taken on aUnicam UV-3 spectrophotometer at a place where it was approximately1.5-2.0 absorbance units, and the spot was marked. The samples were thencured for 75 minutes at 125° C. and the absorbance was remeasured. Thecoating was then etched off with concentrated sulfuric acid, and theabsorbance was measured a third time. These measurements enabledcalculation of the amount of UV absorber that volatilized, that migratedinto the polycarbonate, and (by difference) the amount that remained inthe coating.

Photostability measurements. Small portions (about 1 centimeter×2centimeters) of the above films were mounted on steel frames to makearrays. Absorbance readings were obtained from each film at 325, 328,340, and 345 nanometers using an uncoated polycarbonate film in thereference beam. The appropriate absorbance for each UV absorber (seeTable 1) was plotted as log(10^(A)−1) vs. exposure. The exposure wasexpressed as kilojoules/(meter²-nanometer) (kJ/m² nm) measured at 340nanometers. The slope is the rate of UV absorber photodegradationexpressed as absorbance units per 1000 kJ/m² nm at 340 nm.

The sample array was exposed in an Atlas Ci4000 xenon arc Weather-ometeraccording to the following conditions:

irradiance: 0.75 Watts/meter² @ 340 nm

light period: 100% On

dark/dry: N/A

dark/spray: 30 minutes weekly

light/spray: N/A

black panel: 55° C.

dry bulb: 35° C.

rel. humid.: 30%

inner filter: CIRA

outer filter: Soda lime.

Results, presented in Table 1, show that the triazine UV absorberTINUVIN® 400 was retained well during cure and had a generally low lossrate in coatings made with all three diols. The benzotriazole TINUVIN®384 was retained less well during cure and had a much high loss rate.The benzophenone DHBP was retained well during cure, but was lostquickly during weathering while the benzophenone CYASORB® 531 was notretained well during cure and was lost very rapidly during weathering.The hindered amine light stabilizer had little effect on the UV absorberlosses.

TABLE 1 % UVA in coating loss rate Ex. No. diol UVA HALS post cureA/1000 kJ 1 Desmophen VP LS Tinuvin 400 100 0.06 2391 2 Desmophen VP LSTinuvin 400 0.06 98 0.05 2391 3 Desmophen VP LS Tinuvin 400 0.06 98 0.042391 4 Desmophen S1015- Tinuvin 400 99 0.04 120 5 Desmophen S1015-Tinuvin 400 0.06 99 0.06 120 6 K-Flex UD-320 Tinuvin 400 98 0.06 7K-Flex UD-320 Tinuvin 400 0.06 99 0.06 8 K-Flex UD-320 Tinuvin 400 0.06100 0.06 mean loss rate 0.05 9 Desmophen VP LS Tinuvin 384 78 0.22 239110 Desmophen VP LS Tinuvin 384 0.06 81 0.19 2391 11 Desmophen S1015-Tinuvin 384 75 0.25 120 12 Desmophen S1015- Tinuvin 384 75 0.22 120 13Desmophen S1015- Tinuvin 384 78 0.19 120 14 Desmophen S1015- Tinuvin 3840.06 82 0.19 120 15 Desmophen S1015- Tinuvin 384 0.06 78 0.17 120 16K-Flex UD-320 Tinuvin 384 89 0.17 17 K-Flex UD-320 Tinuvin 384 0.06 860.17 mean loss rate 0.19 18 Desmophen VP LS DHBP 98 0.51 2391 19Desmophen VP LS DHBP 99 0.57 2391 20 Desmophen S1015- DHBP 100 0.43 12021 Desmophen S1015- DHBP 98 0.39 120 22 Desmophen S1015- DHBP 0.06 980.30 120 23 K-Flex UD-320 DHBP 99 0.42 24 K-Flex UD-320 DHBP 99 0.40 25K-Flex UD-320 DHBP 0.06 98 0.43 mean loss rate 0.45 26 Desmophen VP LSCyasorb 531 37 0.71 2391 27 Desmophen VP LS Cyasorb 531 42 1.00 2391 28Desmophen VP LS Cyasorb 531 0.06 47 0.70 2391 29 Desmophen VP LS Cyasorb531 0.06 33 0.68 2391 30 Desmophen S1015- Cyasorb 531 43 0.61 120 31Desmophen S1015- Cyasorb 531 0.06 40 0.72 120 32 Desmophen S1015-Cyasorb 531 0.06 40 0.82 120 33 K-Flex UD-320 Cyasorb 531 73 0.68 34K-Flex UD-320 Cyasorb 531 0.06 70 0.67 35 K-Flex UD-320 Cyasorb 531 0.0668 0.86 mean loss rate 0.75

Examples 36 and 37

Example 2 from Table 1 was reformulated to contain only 2.2% TINUVIN®400 by weight of coating solids to make Example 36. Example 36 andExample 28, containing 5% CYASORB® 531, were flow coated onto 4 inch by12 inch by ⅛ inch (10.16 cm by 30.48 by 0.3175 cm) polycarbonate panels,air dried for 30 minutes, and baked for 60 minutes at 130° C. in aforced air oven. Samples from 3″ below the flow line of the panel (theflow line is the vertical position at which the coating is applied) weresubjected to xenon arc weathering in an Atlas Ci35a xenon arcweatherometer under the conditions shown below:

irradiance: 0.77 Watts/meter² @ 340 nanometers

light period: 160 minutes

dark/dry: 5 minutes

dark/spray: 15 minutes

light/spray: N/A

black panel: 70° C.

dry bulb: 45° C.

relative humidity: 50%

inner filter: Type S borosilicate

outer filter: Type S borosilicate

After an exposure of 6950 kJ/m² nm measured at 340 nm, the Example 36sample with triazine UV absorber had a change in Yellowness Index (ASTMD1925) of −0.14 while the Example 28 sample, made with the benzophenoneUV absorber, had a change in Yellowness Index of +8.3 and suffereddelamination.

This example shows superior weatherability of the coating containing thetriazine UV absorber, even when present in half the loading of abenzophenone UV absorber.

Examples 38-42

Examples 38-42 were made by flow coating 4.5 millimeter thick flatpolycarbonate panels with the coating compositions shown in Table 2,below, letting the coated panels air dry for 20 minutes, and curing themfor 60 minutes at 130° C. The samples varied primarily in the type andamount of polyol compound, the amount of p-toluenesulfonic acid, theamount of triethylamine, the solvent composition, and the amounts oftriazine and hindered amine light stabilizers. Most raw materials werethe same as those used in Examples 1-35. Tone 210 is an aliphaticoligomeric diol supplied by Dow. PTSA is p-toluenesulfonic acid. Allamounts are expressed in parts by weight.

TABLE 2 Ex. 38 Ex. 39 Ex. 40 Ex. 41 Ex. 42 Cymel 303 32.90 32.90 32.9032.90 32.80 Desmophen VP LS 2391 32.90 32.90 32.90 32.90 0.00 Tone 2100.00 0.00 0.00 0.00 24.00 PTSA (20% soln in 8.88 8.88 2.22 2.22 2.49methoxypropanol) Triethylamine 0.00 0.95 0.00 0.24 0.001-Methoxy-2-propanol 37.01 37.01 37.01 37.01 90.00 1-Butoxy-2-propanol37.01 37.01 37.01 37.01 0.00 n-Butanol 4.48 4.48 4.48 4.48 0.00 Methanol3.52 3.52 3.52 3.52 0.00 Efka 30 0.27 0.27 0.27 0.27 0.29 Tinuvin 4001.74 1.74 1.74 1.74 2.82 Tinuvin 152 0.19 0.19 0.19 0.19 0.30

All panels were subjected to the Taber abrasion test (ASTM D1044 at 100cycles, 500 gram load, CS10F wheels). Haze was measured according toASTM D1003 prior to the test and after the test. The test was done on 3panels and the average haze increase is reported in the Table 3. Theresults show that all samples meet the initial abrasion resistancerequirements of ANSI/SAE Z26.1-1996 Item 4 for safety glazing materials.

TABLE 3 Ex. 38 Ex. 39 Ex. 40 Ex. 41 Ex. 42 Delta Haze [%] 5.8 4.2 5.53.3 9.1

For the formability test, all panels were pre-heated in an oven at 160°C. and molded over a 4 inch diameter mandrel. Samples 38, 39, 40 and 41showed no cracking whereas sample 42 showed two small edge cracks aftermolding.

Examples 43-45

Examples 43-45 were prepared by flow coating 5 millimeter thick by 600millimeter wide by 2000 millimeter high flat polycarbonate panels withthe coating compositions shown in Table 4, below, letting the coatedpanels air dry for 20 min and curing them for 60 min at 130° C. CYMEL®301 is hexamethoxymethylmelamine, a product of Cytec.

TABLE 4 Ex. 43 Ex. 44 Ex. 45 Cymel 301 0.00 0.00 13.53 Cymel 303 15.5415.50 0.00 Desmophen S-1015-120 0.00 0.00 10.14 Desmophen VP LS 239115.54 15.50 0.00 PTSA (20% in methoxypropanol) 1.52 1.51 0.36Triethylamine 0.00 0.25 0.00 Tinuvin 400 0.87 0.87 0.00 Tinuvin 123 0.080.08 0.00 Efka 30 0.13 0.13 0.18 DHBP 0.00 0.00 1.35 1,2-butanediol 0.000.00 8.68 1-Methoxy-2-propanol 45.79 45.67 47.74 1-Butoxy-2-propanol16.88 16.84 18.02 n-Butanol 2.05 2.04 0.00 Methanol 1.62 1.61 0.00

All panels were subjected to the Taber abrasion test (ASTM D1044 at 100cycles, 500 gram load, CS10F wheels). Haze increase is reported in theTable 5. In Table 5, “Delta Haze Top” refers to measurements on samplesapproximately 2-12 centimeters below the flow line, and “Delta HazeBottom” refers to measurements on samples approximately 2-12 centimetersabove the bottom of the sheet. The results show that all samples meetthe initial abrasion resistance requirements of ANSI/SAE Z26.1-1996 Item4 for safety glazing materials.

Formability was measured by heating 12 sheets, 100 millimeters by 300millimeters in size, in an oven at 160° C. and molding them overmandrels of 100 millimeter and 150 millimeter radii. Even the slightestcracking of the coating was considered a failure. In Table 5, thepercentage of sheets that passed the formability test is reported. Theresults show that Examples 43 and 44 had superior formability whilemaintaining or improving abrasion resistance compared with Example 45.

TABLE 5 Ex. 43 Ex. 44 Ex. 45 Delta Haze Top [%] 8.9 6 9.6 Delta HazeBottom [%] 7.8 4.8 8.3 Formability @ 100 mm [%] 75 58 0 Formability @150 mm [%] 100 100 75

Examples 46-54

Coating solutions with the formulations shown in Table 6 were prepared(all amounts are expressed in parts by weight). Tone 301, Tone 305 andTone 310 are trifunctional, oligomeric polycaprolactones obtained fromDow. DESMOPHEN® F2037-420 is an aliphatic polyester triol from Bayer.Polycarbonate sheet was coated by dipping it in the coating solution,letting it air dry for 20 minutes at room temperature, and curing it at130° C. for 60 minutes.

TABLE 6 Component Ex. 46 Ex. 47 Ex. 48 Ex. 49 Ex. 50 Ex. 51 Ex. 52 Ex.53 Ex. 54 Cymel 303 25.78 25.78 25.78 25.78 25.78 25.78 25.78 25.7825.78 Desmophen VP LS 25.70 19.30 19.30 19.30 19.30 21.80 21.80 21.8021.80 2391 Desmophen F2037- 0.00 6.40 0.00 0.00 0.00 3.90 0.00 0.00 0.00420 Tone 301 0.00 0.00 6.40 0.00 0.00 0.00 3.90 0.00 0.00 Tone 305 0.000.00 0.00 6.40 0.00 0.00 0.00 3.90 0.00 Tone 310 0.00 0.00 0.00 0.006.40 0.00 0.00 0.00 3.90 20% p-toluenesulfonic 4.38 4.38 4.38 4.38 4.384.38 4.38 4.38 4.38 acid in 2-propanol Efka 30 0.11 0.11 0.11 0.11 0.110.11 0.11 0.11 0.11 Tinuvin 400 1.37 1.37 1.37 1.37 1.37 1.37 1.37 1.371.37 Tinuvin 152 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.151-methoxy-2-propanol 29.00 29.00 29.00 29.00 29.00 29.00 29.00 29.0029.00 1-butoxy-2-propanol 29.00 29.00 29.00 29.00 29.00 29.00 29.0029.00 29.00 1-butanol 6.45 6.45 6.45 6.45 6.45 6.45 6.45 6.45 6.45

Chemical resistance of the coated sheets was analyzed by application ofan acetone drenched cloth and visual analysis after removal of thecloth. The analysis was done after 2, 3, 4, and 5 min applicationrespectively. The results are reported as “P” when no visual change ofthe coating was observed, “JS” when the coating was just starting towrinkle and “F” when the coating was obviously damaged. The results areshown in Table 7.

TABLE 7 Acetone resistance Ex. 46 Ex. 47 Ex. 48 Ex. 49 Ex. 50 Ex. 51 Ex.52 Ex. 53 Ex. 54 2 min P P P P P P P P P 3 min P P P P P P P P P 4 minJS P P P P P P P P 5 min JS P P P JS F P JS JS

From these examples it is clear that addition of trifunctional oligomersincreases the chemical resistance of the coating towards acetonecompared with Example 46.

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

All cited patents, patent applications, and other references areincorporated herein by reference in their entirety.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext.

1. A method of producing a sheet, comprising: coating a curablecomposition on a face of a polycarbonate sheet, wherein the curablecomposition comprises an aminoplast resin, a polyol compound, and aUV-absorbing amount of a triazine compound having the structure

wherein each occurrence of Ar is independently phenyl or substitutedphenyl; wherein the substituents on the phenyl group may be hydroxy,amino, C₁-C₁₂ hydrocarbyl, C₁-C₁₂ hydrocarbyloxy, or C₁-C₁₂hydrocarbylamino; and R⁸ is hydrogen or C₁-C₁₆ hydrocarbyl wherein thehydrocarbyl group may contain nitrogen or oxygen heteroatoms; and curingthe curable composition to form a protective layer.
 2. The method ofclaim 1, wherein said coating comprises flow coating.
 3. The method ofclaim 1, wherein said coating comprises dip coating.
 4. The method ofclaim 1, wherein the aminoplast resin is a melamine-formaldehyde resinhaving the structure

wherein each occurrence of R¹ is independently hydrogen, a methylenebridge to another melamine nucleus, or CH₂OR², wherein R² is hydrogen orC₁-C₁₂ alkyl.
 5. The method of claim 1, wherein the curable compositioncomprises about 20 to about 80 weight percent of the aminoplast resin,based on the total weight of curable solids.
 6. The method of claim 1,wherein the polyol compound comprises an oligomeric aliphaticpolycarbonate diol, an oligomeric aliphatic polyestercarbonate diol, anoligomeric aliphatic polyurethane diol, or a mixture thereof.
 7. Themethod of claim 1, wherein the polyol compound comprises an oligomericaliphatic polycarbonate diol.
 8. The method of claim 1, wherein thepolyol compound comprises an oligomeric aliphatic polyestercarbonatediol.
 9. The method of claim 1, wherein the polyol compound comprises anoligomeric aliphatic polyurethane diol; and wherein the oligomericaliphatic polyurethane diol has the structure

wherein R⁴ is the residuum of a diol comprising at least 50% by numberaliphatic diols in which the two hydroxyl groups are separated by atleast two intervening carbon atoms; R⁶ is the residuum of a diisocyanatecompound comprising at least 50% by number aliphatic diisocyanates inwhich the two isocyanate groups are separated by at least twointervening carbon atoms; and p is 2 to about
 20. 10. The method ofclaim 1, wherein the polyol compound comprises a diol and a triol. 11.The method of claim 1, wherein the curable composition comprises about20 to about 80 weight percent of the polyol, based on the total weightof curable solids.
 12. The method of claim 1, wherein the curablecomposition comprises about 0.1 to about 10 weight percent of thetriazine, based on the total weight of curable solids.
 13. The method ofclaim 1, wherein the curable composition further comprises a hinderedamine light stabilizer.
 14. The method of claim 1, wherein the curablecomposition further comprises a solvent selected from the groupconsisting of C₁-C₁₂ alcohols, C₃-C₁₂ ketones, C₃-C₁₂ esters, C₄-C₁₂ethers, C₃-C₁₂ alkoxy alkanols, C₁-C₁₂ halogenated hydrocarbons, C₂-C₁₂carboxylic acids, C₆-C₁₈ aromatic compounds, and mixtures thereof. 15.The method of claim 14, wherein the solvent comprises1-methoxy-2-propanol, 1-butoxy-2-propanol, or a mixture thereof.
 16. Themethod of claim 1, wherein the curable composition further comprises acuring catalyst selected from the group consisting of alkyl acidphosphates, dialkyl acid phosphates, phosphoric acid, maleic acid,maleic anhydride, fumaric acid, chloromaleic acid, chloromaleicanhydride, alkyl acid phthalates, monoalkyl succinates, monoalkylmaleates, alkyl sulfonic acids, aryl sulfonic acids, sulfamic acid, andmixtures thereof.
 17. The method of claim 1, wherein the curablecomposition further comprises a catalyst stabilizer selected from thegroup consisting of triethylamine, pyridine, 2-methylaminoethanol, andmixtures thereof.
 18. The method of claim 1, wherein the protectivelayer has a thickness of about 2 to about 40 micrometers.
 19. The methodof claim 1, wherein the aminoplast resin is a melamine-formaldehyderesin having the structure

wherein each occurrence of R¹ is independently hydrogen, a methylenebridge to another melamine nucleus, or CH₂OR², wherein R² is hydrogen orC₁-C₁₂ alkyl; wherein the polyol compound comprises an oligomericaliphatic polyestercarbonate diol having a number average molecularweight of at least 200 atomic mass units; and wherein the protectivelayer has a thickness of about 2 to about 40 micrometers.
 20. The methodof claim 19, wherein the curable composition further comprises ahindered amine light stabilizer.